This invention relates to a point of lubrication flow indicator, in particular this invention relates to a piston-type flow switch and an improvement thereof.
In a piston-type flow switch a plunger is placed directly in the fluid flow stream flowing through a barrel-like body. As flow increases, the flow, impinging upon a first end of the plunger, pushes the plunger against the bias of a spring until the plunger passes and uncovers a port. This plunger abuts at a second end, a magnetic piston. The resultant movement of the magnetic piston influences a magnetic reed switch mounted to an outside of the barrel-like body adjacent to the magnetic piston but not exposed to the fluid stream. Once the plunger passes the port, lubrication fluid can then flow from one end of the barrel-like body, through the port and downstream, past the magnetic piston and out of the body to the point of lubrication. When flow stops, the spring pushes the piston and plunger back and closes the reed switch. The magnetic piston must fit loosely enough so that the lubricant can flow pass the magnetic piston and also so that lubricant can leak past the magnetic piston and allow the magnetic piston to retract. Some designs use carefully sizes holes in the piston to accomplish this task.
This design of the piston-type flow switch tends to be very sensitive to viscosity and to flow rate. While a piston-type flow switch designed for very low flow rate could operate at a higher flow rate, it would present a very high pressure drop in the small passages such as the holes in the piston. Several range variations of this sensor would, almost certainly, be required.